Aline Rougier

Metal hydrides for lithium-ion batteries

Classical electrodes for Li-ion technology operate via an insertion/de-insertion process. Recently, conversion electrodes have shown the capability of greater capacity, but have so far suffered from a marked hysteresis in voltage between charge and discharge, leading to poor energy efficiency and voltages. Here, we present the electrochemical reactivity of MgH(2) with Li that constitutes the first use of a metal-hydride electrode for Li-ion batteries. The MgH(2) electrode shows a large, reversible capacity of 1,480 mAh g(-1) at an average voltage of 0.5 V versus Li(+)/Li(o) which is suitable for the negative electrode. In addition, it shows the lowest polarization for conversion electrodes. The electrochemical reaction results in formation of a composite containing Mg embedded in a LiH matrix, which on charging converts back to MgH(2). Furthermore, the reaction is not specific to MgH(2), as other metal or intermetallic hydrides show similar reactivity towards Li. Equally promising, the reaction produces nanosized Mg and MgH(2), which show enhanced hydrogen sorption/desorption kinetics. We hope that such findings can pave the way for designing nanoscale active metal elements with applications in hydrogen storage and lithium-ion batteries.

The cycling properties of the LixNi1−yCoyO2 electrode

The LiNiO2LiCoO2 system exhibits a complete solid solution. These materials crystallize in the rhombohedral system with a layered structure. They have been used as positive electrode in lithium batteries. Up to 0.5 lithium atom can be reversibly deintercalated in the 3.5 to 4.0 V potential range. The highest specific energy (close to 500 W h/kg) is obtained in the LixNi0.7Co0.3O2 system. Moreover, the very small volume change upon deintercalation increased their interest for application point of view.

An overview of the Li(Ni,M)O2 systems: syntheses, structures and properties

Lithium nickel oxide derivatives are promising positive electrode materials for the next generation of lithium-ion batteries. Partial substitution of certain cations for nickel in this family of oxides significantly modifies their properties and is therefore an attractive route to develop an optimised oxide electrode which satisfies the demanding requirements for rechargeable battery applications. In this paper the interest is focused on the effect of cobalt, iron, aluminium and magnesium for a general discussion of the effect of cationic substitution on the properties based on a review of results mostly obtained in our laboratories. Although iron substitution does not seem interesting for the practical aspect, iron Mossbauer spectroscopy allows very precise characterisations, interesting to understand the general behaviour of this family of materials. We deal with the optimisation of the synthesis conditions in order to obtain the most electrochemically active materials. The relations between the nature of the substituting cation, the presence of foreign cations in the lithium site, the electrochemical behaviour and the redox processes upon electrochemical cycling are discussed in detail. A new view of the relation between this latter point and the cationic distribution formed during the material synthesis is proposed.

Non-cooperative Jahn-Teller effect in LiNiO2 : an EXAFS study

Lithium nickel oxide, used as positive electrode in rechargeable lithium batteries, exhibits a layered structure made of NiO2 slabs between which Li+ ions are inserted in an octahedral environment. In fact, stoichiometric LiNiO2 has never been reported, the true formula is Li1−zNi1+zO2 (0.0<z≤0.20). z depending on the experimental conditions. Special attention devoted to the synthesis conditions, has allowed us to obtain quasi-2D LiNiO2. EXAFS spectroscopy shows clearly the existence of two different NiO bond lengths: at 1.91 A (for four of them) and 2.09 A for the two last ones. This local distortion of the NiO6 octahedra results from the Jahn-Teller effect of the trivalent nickel ion in the low spin state t26e1.

Electrochemical Behavior of Iron‐Substituted Lithium Nickelate

Lamellar phases with nominal composition Li(Ni 1-y Fe y )O 2 (y ≤ 0.30) were synthesized and characterized by Rietveld refinement of their X-ray diffraction (XRD) patterns. These materials exhibited the formula Li 1-z (Ni 1-y Fe y ) 1+z O 2 with 0.06 ≤ z ≤ 0.08 and were used as positive electrodes in lithium batteries. Their electrochemical performances decreased with increasing iron content. The Li x (Ni 0.90 Fe 0.10 ) 1.06 O 2 phases were characterized by XRD and Mossbauer spectroscopy. A solid solution appeared in the entire deintercalation domain 0.28 ≤ x ≤ 0.94, and Rietveld refinement of the XRD patterns allowed us to characterize the variation of structural parameters upon lithium deintercalation. 57 Fe Mossbauer spectroscopy showed that nickel and iron ions were oxidized simultaneously. The fraction of high-spin Fe 4+ was related to the strong ligand field resulting from the presence of the prevailing Ni 3+ and Ni 4+ ions which lead to a lattice contraction. The behavior upon deintercalation of the Li(Ni 0.90 Fe 0.10 )O 2 phase was compared to that of two-dimensional LiFeO 2 .

Effect of iron on the electrochemical behaviour of lithium nickelate: from LiNiO2 to 2D-LiFeO2

Abstract Iron substituted lithium nickelate have been obtained by high temperature solid state chemistry. The general formula deduced from structural analysis is Li 1− z (Ni 1− y Fe y ) 1+ z O 2 . Layered phases are obtained for y ≤0.30. The Rietveld refinements of the X-ray diffraction patterns show that, in normal synthesis conditions, the amount of 3d cations in the lithium plane ranges between 0.06 and 0.08. The neutron diffraction study of a material which contains a large amount of extra-cations ( z =0.14) shows that there is no lithium ions in the nickel plane; i.e. there is no cationic mixing. The comparative Mossbauer study of lithium phases with homologous strict 2D sodium phases shows that a small amount of iron ions is in the lithium plane in good agreement with the result previously reported by Reimers and Dahn [1] . The electrochemical behaviour of these materials has been studied in lithium batteries. The reversible capacity is small vs. unsubstituted phases. A Mossbauer spectroscopy study has shown that iron and nickel are simultaneously oxidised upon lithium deintercalation. The electrochemical behaviour of these materials has been compared to that of layered LiFeO 2 and NaFeO 2 .

Low-Cost and Facile Synthesis of the Vanadium Oxides V2O3, VO2, and V2O5 and Their Magnetic, Thermochromic and Electrochromic Properties

In this study, vanadium sesquioxide (V2O3), dioxide (VO2), and pentoxide (V2O5) were all synthesized from a single polyol route through the precipitation of an intermediate precursor: vanadium ethylene glycolate (VEG). Various annealing treatments of the VEG precursor, under controlled atmosphere and temperature, led to the successful synthesis of the three pure oxides, with sub-micrometer crystallite size. To the best of our knowledge, the synthesis of the three oxides V2O5, VO2, and V2O3 from a single polyol batch has never been reported in the literature. In a second part of the study, the potentialities brought about by the successful preparation of sub-micrometer V2O5, VO2, and V2O3 are illustrated by the characterization of the electrochromic properties of V2O5 films, a discussion about the metal to insulator transition of VO2 on the basis of in situ measurements versus temperature of its electrical and optical properties, and the characterization of the magnetic transition of V2O3 powder from SQUID measurements. For the latter compound, the influence of the crystallite size on the magnetic properties is discussed.

Environmental assessment of electrically controlled variable light transmittance devices

A comprehensive benchmark analysis has been performed on five electrically controlled state-of-the-art transmittance modulation devices including their production routes, from ‘cradle-to-gate’. The benchmarks have been modeled employing the GaBi life cycle assessment software tool, which successfully yielded the most important environmental problem areas for the product life cycles of electrochromic and electrotropic light-modulating devices. In terms of the energy demand of processing, all-solid-state technology was found to be less favorable than wet-chemical electrodeposition processes; however, the effect is interestingly overcompensated for by the resource depletion resulting from higher layer thicknesses in the latter case. As opposed to the mineral-glass based benchmarks, a plastic-film based system was particularly favorable, implying that the substrate is a factor with a strong environmental impact in transmittance modulation devices. Eventually, very high impacts were found for tin-doped indium oxide (ITO) and iridium oxide, i.e. a common transparent conductor and anodic electrochromic material, respectively. The results obtained support important current trends such as in-line manufacturing of electrochromic devices, the quest for ITO replacement materials, and, in general, the replacement of energy- and resource-intensive processes (sputter deposition of heavy metal oxides) by less demanding methods.

Double-Sided Electrochromic Device Based on Metal–Organic Frameworks

Devices displaying controllably tunable optical properties through an applied voltage are attractive for smart glass, mirrors, and displays. Electrochromic material development aims to decrease power consumption while increasing the variety of attainable colors, their brilliance, and their longevity. We report the first electrochromic device constructed from metal organic frameworks (MOFs). Two MOF films, HKUST-1 and ZnMOF-74, are assembled so that the oxidation of one corresponds to the reduction of the other, allowing the two sides of the device to simultaneously change color. These MOF films exhibit cycling stability unrivaled by other MOFs and a significant optical contrast in a lithium-based electrolyte. HKUST-1 reversibly changed from bright blue to light blue and ZnMOF-74 from yellow to brown. The electrochromic device associates the two MOF films via a PMMA-lithium based electrolyte membrane. The color-switching of these MOFs does not arise from an organic-linker redox reaction, signaling unexplored possibilities for electrochromic MOF-based materials.

Electrochemical Property Assessment of Pr2CuO4 Submicrofiber Cathode for Intermediate-Temperature Solid Oxide Fuel Cells

The Pr2CuO4 (PCO) submicrofiber precursors are prepared by electrospinning technique and the thermo-decomposition procedures are characterized by thermal gravity (TG), X-ray diffraction (XRD), Fourier transform infrared spectoscopy (FT-IR), and scanning electron microscopy (SEM), respectively. The fibrous PCO material was formed by sintering the precursors at 900 °C for 5 hrs. The highly porous PCO submicrofiber cathode forms good contact with the Ce0.9Gd0.1O1.95 (CGO) electrolyte after heat-treated at 900 °C for 2 hrs. The performance of PCO submicrofiber cathode is comparably studied with the powder counterpart at various temperatures. The porous microstructure of the submicrofiber cathode effectively increases the three-phase boundary (TPB), which promotes the surface oxygen diffusion and/or adsorption process on the cathode. The PCO submicrofiber cathode exhibits an area specific resistance (ASR) of 0.38 Ω cm2 at 700 °C in air, which is 30% less than the PCO powder cathode. The charge transfer process is the rate limiting step of the oxygen reduction reaction (ORR) on the submicrofiber cathode. The maximum power densities of the electrolyte-support single cell PCO|CGO|NiO-CGO reach 149 and 74.5 mW cm−2 at 800 and 700 °C, respectively. The preliminary results indicate that the PCO submicrofiber can be considered as potential cathode for intermediate temperature solid fuel cells (IT-SOFCs).